1. Field of the Invention
The present invention relates to methods of making semiconductor devices using light emitting organic materials, and more specifically, to methods which involve the modification of the properties of an organic film after it has been deposited by either: (i) adding new components into the film from a top or bottom surface; or (ii) by causing components to leave the film from a top or bottom surface.
2. Related Art
Polymers and blends of polymers and small organic molecules have recently been extensively used to fabricate organic light emitting diodes and thin film transistors.
Organic films are typically deposited in thin film form for electrical and optoelectronic applications by uniformly coating a surface by spin-coating or other methods. Sometimes the final organic film itself is not directly formed, but a precursor is deposited which is converted to a polymer by a subsequent step, such as heating or exposure to UV light (e.g. PPV). It is also well known that adding various elements to the organic film can change its electrical and/or optical properties. These may include elements to change the conduction of electrical carriers (e.g. PBD for electron transportability), or dye centers to change the color of photo- and electro-luminescence (e.g. coumarin 6 in PVK). These extra elements are usually added to the original material before the final solid film is deposited. For example, these different groups could be bonded to a polymer chain before the polymer is deposited by spin coating, or may just be added as other polymers or individual smaller molecules to the solution containing the polymer before a thin film is formed. In either case all materials in the original solution become part of the final film.
The goal of fabricating full color flat panel displays has the potential to be reached using organic light emitting diodes (OLEDs). The difficulty with using this technology is that the current deposition techniques, such as spin-coating and evaporation, deposit blanket films. The film can be used to make devices of a single color. To achieve individual emitters of different color next to each other, such as red, green, and blue, the deposited blanket film must be typically etched into a pattern, as might be done by photolithography followed by etching. Then, this process has to be repeated for multiple layers to achieve full color (red, green and blue emitters). Etching of organic films and photoresist processing for lithography on organic films has proven to be technically very difficult and expensive. Therefore, instead of making a blanket film of one color, etching and making a blanket film of another color, it would be beneficial to make one blanket film and later locally change the properties of the film to emit different light colors. Thus, the need for etching would be removed.
Another approach is ink-jet printing local regions, but a problem associated with ink-jetting printing is that the dots printed do not have a uniform thickness.
Accordingly, what is desired, and has not heretofore been developed, is a method to modify the properties of a film after it has been formed, by introducing therein or removing impurities to modify the properties therefrom.